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走り出す， 走りだす， はしりだす
1. to begin to run, to start running, to break into a run
tbd
は
1. indicates sentence topic
2. indicates contrast with another option (stated or unstated)
3. adds emphasis
指示句子的主题；表示与另一选项（无论是否明确提及）形成对比；表示强调
